1. Field of the Invention
The present invention relates to centrifuge tubes and, more particularly, to the sealing or closing of centrifuge tubes.
2. Description of Related Art
Typical centrifuge tubes have a generally cylindrical body with one end having an filler opening or tube stem to receive the fluid sample to be subject to centrifugation. After the introduction of the fluid sample into the tube, it is necessary to provide a very tight closure or capping means over the open-end of the tube in order to prevent leakage of the contents during centrifugation.
A continual problem with the placement of capping means on the open-ended centrifuge tubes is ensuring that a proper seal is being achieved between the plug and the tube to prevent any possible or potential leakage which could occur under hydrostatic pressure build up within the tube. Hydrostatic pressure within the tube becomes extremely strong when the centrifuge is rotated at speeds of 20,000 rpm or greater.
The significance of eliminating or preventing any potential leakage in a high speed centrifuge cannot be under estimated. The fluid sample may contain some type of pathogen, mutagen, bacteria or other hazardous material. Leakage during the centrifugation run can create a hazardous condition for the operator. The sample may be a small supply of material which cannot be replaced, which the user does not wish to lose through leakage during the centrifugation run. Further, leakage will cause rotor imbalance and result in rotor mishap.
In many instances, the resulting leakage is caused by an improper seal being achieved between the capping means and the centrifuge tube because of either a poor configuration or design of the capping means, or as a result of the improper placement of the capping means on the centrifuge tube. Not only is it important that the capping means be designed to achieve a secure seal between the test tube and the capping means, but also it is important that the capping means have such a design that it is easy to remove after the centrifuge run without having to disturb the contents of the fluid sample after the centrifugation. Otherwise, the separated sample constituents may be remixed and invalidate the centrifugation run.
U.S. Pat. No. 5,127,895 discloses a self-sealing centrifuge tube which makes use of the hydrostatic pressure of the sample solution contained in the tube to engage a tight seal during centrifugation. This patent has been assigned to the assignee of the present invention, and is incorporated by reference herein. The tube stem of the centrifuge tube is capped with a plug and locked into the rotor cavity with a nut and spacer prior to centrifugation. Upon centrifugation, hydrostatic pressure which occurs as a result of a centrifugal force on the solution causes the tube stem to press on the plug against the support provided by the spacer fixed in place within the cavity or the centrifugal weight of the plug. As a result, a seal is formed between the plug and the tube stem. As centrifugal forces increase with an increase in rotor speed, the hydrostatic pressure increases thereby forcing a tighter seal of the plug against the tube stem. The sealing force is therefore commensurated with the magnitude of hydrostatic pressure which is dependent on the centrifugal force experienced by the sample solution contained in the tube. After centrifugation, a weak seal remains between the plug and the filler stem, making it easy for the user to unplug the centrifuge tube without requiring any special tools. The afore-described tube and closure has been commercialized by Beckman Instruments, Inc., California, U.S.A. under the trademark OptiSeal.TM..
While the patented self-sealing centrifuge tube and closure provides an excellent seal during centrifugation, it has been found that residual pressure built up within the centrifuge tube due to deformation of the centrifuge tube caused by centrifugation might eject the plug during handling of the centrifuge tube after centrifugation.